Method and system for power optimization for a global navigation satellite system

ABSTRACT

Methods and systems for power optimization of a global navigation satellite system may comprise receiving LEO RF satellite signals utilizing a LEO satellite signal receiver path (LEO Rx) in a wireless communication device (WCD). Circuitry in the LEO Rx may be configured in a powered down state based on a sleep schedule. A location of the wireless communication device may be determined utilizing LEO signals received by the LEO Rx. The sleep schedule may be based on a desired accuracy of the determined location, the relative strengths of signals received from a plurality of LEO satellites, a relevance factor generated by a position engine and communicated to the sort module, or a desired power level of the WCD. The relative strengths of received signals may be compared utilizing a sort module in a LEO demodulator in the LEO satellite signal receiver path.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application makes reference to and claims priority to U.S.Provisional Application Ser. No. 61/552,682 filed on Oct. 28, 2011, U.S.Provisional Application No. 61/552,729 filed on Oct. 28, 2011, U.S.Provisional Application No. 61/569,639 filed on Dec. 12, 2011, U.S.Provisional Application No. 61/623,026 filed on Apr. 11, 2012, and U.S.Provisional Application No. 61/664,503 filed on Jun. 26, 2012.

This application also makes reference to U.S. application Ser. No.12/965,805 filed on Dec. 10, 2010.

Each of the above identified applications is hereby incorporated hereinby reference in its entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to wireless communication.More specifically, certain embodiments of the invention relate to amethod and system for power optimization of a global navigationsatellite system.

Global navigation satellite systems (GNSS) such as the NAVSTAR globalpositioning system (GPS) or the Russian GLONASS provide accuratepositioning information for a user anywhere on Earth that GNSS signalsmay be received. GNSS satellites are medium Earth orbit (MEO)satellites, about 12,000 miles above the surface. Highly accurate GNSSclock signals from these satellites may be used to accurately determinethe position of a receiver.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with the present invention as set forth inthe remainder of the present application with reference to the drawings.

A system and/or method for power optimization of a global navigationsatellite system, substantially as shown in and/or described inconnection with at least one of the figures, as set forth morecompletely in the claims.

Various advantages, aspects and novel features of the present invention,as well as details of an illustrated embodiment thereof, will be morefully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a diagram illustrating an exemplary wireless device with aglobal navigation satellite system, in accordance with an embodiment ofthe invention.

FIG. 1B is a block diagram of an exemplary dual mode global navigationsatellite system for automated syncing in accordance with an embodimentof the invention.

FIG. 1C is a schematic illustrating power optimization of a low Earthorbit (LEO) satellite receiver, in accordance with an embodiment of theinvention.

FIG. 1D illustrates an exemplary low Earth orbit satellite system, inaccordance with an embodiment of the invention.

FIG. 2A is a diagram illustrating an exemplary dual mode radio frequencyreceiver, in accordance with an embodiment of the invention.

FIG. 2B is a block diagram illustrating a dual-mode time-division duplexsatellite receiver, in accordance with an embodiment of the invention.

FIG. 3 is a schematic illustrating an exemplary satellite selectionsystem, in accordance with an embodiment of the invention.

FIG. 4 is a schematic illustrating a LEO-assisted GNSS receiver hotstart, in accordance with an embodiment of the invention.

FIG. 5 is a timing diagram illustrating signal pulses from threesatellite vehicles, in accordance with an embodiment of the invention.

FIG. 6 is a timing diagram of signal pulses from three satellites withvarying signal strengths, in accordance with an embodiment of theinvention.

FIG. 7 is a flow diagram illustrating an exemplary satellite signalselect process, in accordance with an embodiment of the invention.

FIG. 8 illustrates exemplary steps for power saving in a low Earth orbitsatellite positioning receiver, in accordance with an embodiment of theinvention.

FIG. 9 illustrates exemplary steps for satellite positioning receiversleep scheduling, in accordance with an embodiment of the invention.

FIG. 10 is a block diagram illustrating an exemplary LEO satellitereceiver information flow, in accordance with an embodiment of theinvention

FIG. 11 is a block diagram illustrating an exemplary satellite framesequence, in accordance with an embodiment of the invention.

FIG. 12 is an exemplary satellite burst schedule, in accordance with anembodiment of the invention

DETAILED DESCRIPTION OF THE INVENTION

Certain aspects of the invention may be found in a method and system forpower optimization of a global navigation satellite system. Exemplaryaspects of the invention may comprise receiving LEO RF satellite signalsutilizing a LEO satellite signal receiver path in a wirelesscommunication device. A location of the wireless communication devicemay be determined utilizing LEO signals received by the LEO satellitesignal receiver path. Circuitry in the LEO satellite signal receiverpath may be configured in a powered down state based on a sleepschedule. The sleep schedule may be based on a desired accuracy of thedetermined location. The sleep schedule may be based on relativestrengths of signals received from a plurality of LEO satellites. Therelative strengths of received signals may be compared utilizing a sortmodule in a LEO demodulator in the LEO satellite signal receiver path.The sleep schedule may be based on a relevance factor generated by aposition engine and communicated to the sort module. The sleep schedulemay be received from a server. The sleep schedule may be based on adesired power level of the wireless communication device. In-phase andquadrature signals may be processed in the LEO satellite signal receiverpath. The wireless device may comprise a medium Earth orbit (MEO)satellite signal receiver path. The wireless communication device may becontrolled by a reduced instruction set computing (RISC) centralprocessing unit (CPU).

As utilized herein, “and/or” means any one or more of the items in thelist joined by “and/or”. As an example, “x and/or y” means any elementof the three-element set {(x), (y), (x, y)}. As another example, “x, y,and/or z” means any element of the seven-element set {(x), (y), (z), (x,y), (x, z), (y, z), (x, y, z)}. As utilized herein, the terms “block”and “module” refer to functions than can be implemented in hardware,software, firmware, or any combination of one or more thereof. Asutilized herein, the term “exemplary” means serving as a non-limitingexample, instance, or illustration. As utilized herein, the term “e.g.,”introduces a list of one or more non-limiting examples, instances, orillustrations.

FIG. 1A is a diagram illustrating an exemplary wireless device with aglobal navigation satellite system, in accordance with an embodiment ofthe invention. Referring to FIG. 1A, there is shown a satellitenavigation system 120 comprising a wireless communication device 101, abuilding 103, medium Earth orbit (MEO) satellites 105, and low Earthorbit (LEO) satellites 107. There is also shown the approximate heightin miles of medium Earth and low Earth satellites of ˜12,000 miles and˜500 miles, respectively.

The wireless communication device 101 may comprise any device or vehicle(e.g. smart phone) where its user may desire to know the location ofsuch device or vehicle. The handheld communication device 101 maycomprise a global navigation satellite system (GNSS) receiver having aconfigurable RF path that may be operable to receive medium Earth orbit(MEO) satellite signals and low Earth orbit (LEO) satellite signals. Inanother exemplary scenario, the wireless communication device 101 maycomprise two RF paths to receive different satellite signals.

The MEO satellites 105 may be at a height of about 12,000 miles abovethe surface of the Earth, compared to about 500 miles above the surfacefor the LEO satellites 107. Therefore, the signal strength of LEOsatellite signals is much stronger than MEO satellite signals. The LEOsatellites 107 may typically be used for telecommunication systems, suchas Iridium satellite phones, whereas the MEO satellites 105 may beutilized for location and navigation applications.

In certain circumstances, MEO signals, such as GPS signals, may beattenuated by buildings or other structures to such an extent that GPSreceivers cannot obtain a lock to any GPS satellites. However, due tothe stronger signal strength of LEO satellite signals, the LEO signalsmay be utilized by devices to supplement or substitute the MEO satellitesignals in the devices. However, the frequencies utilized for MEO andLEO satellite communication are not the same, so a conventional GPSreceiver cannot process LEO signals.

In an exemplary embodiment, the wireless communication device 101 may beoperable to receive both LEO satellite signals, such as Iridium signals,and MEO signals, such as GPS signals. In this manner, the receiver maybe able to determine the user's location despite having high attenuationof GPS signals to below that of the sensitivity of a conventional GPSreceiver. Thus, the wireless communication device 101 may be able toaccurately determine its location by receiving either or both Iridiumand GPS satellite signals. This may be enabled by utilizing separate RFpaths, one path configured to receive MEO signals and the other pathconfigured to receive LEO satellite signals.

In an exemplary scenario, the two separate RF paths may share somefront-end components, such as an antenna, low-noise amplifier (LNA), anda splitter, for example. In this scenario, the shared front-endcomponents may comprise enough bandwidth to process both MEO and LEOsignals. In another exemplary scenario, the wireless device may utilizeseparate front-end components. Furthermore, in instances where only onetype of signal is to be received, the inactive RF path may be powereddown to conserve power.

In yet another exemplary scenario, the separate RF paths may betime-division duplexed (TDD), or selectively enabled, such that both MEOand LEO signals may be received, but at alternating times. This mayenable MEO-assisted LEO positioning or LEO-assisted MEO positioning, forexample. The wireless communication device 101 may comprise a blankingor switching module for enabling TDD signal reception, where the TDDprocess may be carried out in the digital domain. For example, the MEO,or GPS, processing path may be blanked, i.e. set to and held at the lastsampled value, while the LEO path receives and demodulates LEO signals.

Determining the location of the wireless device using stronger LEOsatellite signals, particularly when coarse location is acceptable, usesmuch less power than weaker MEO (e.g. GPS) satellite signals,particularly with fine location calculations. Further power savings, indevices that also include a WiFi interface, may be enabled by disablingthe WiFi RF and processor circuitry in the wireless device andconfiguring the WiFi circuitry to only activate when in the vicinity ofa known or trusted WLAN. Trusted WLAN may comprise networks where theuser of the wireless device has an authorized account, such as at a homeor work location, or at a location frequented by the user, such as acoffee shop or hotel.

The wireless communication device 101 may be operable to switch certainfunctionality and/or circuitry off and on based on a sleep schedule. Forexample, Rx circuitry in the LEO signals receiver path may be switchedoff during times when the sleep schedule indicates that no LEO satellitebursts are to be received. Furthermore, in the case of a dual LEO/MEOreceiver, RF circuitry in the MEO signal receiver path may be switchedoff when the received MEO signals are below the sensitivity level. Inthis case, only the LEO signals receiver path may be enabled. The sleepschedule may be configured based on a desired accuracy, where fewerbursts and/or satellites may be utilized for lower accuracyrequirements. Similarly, memory blocks may be powered down when loweraccuracy, and thus lower burst count, operation is acceptable.

In an exemplary scenario, a LEO satellite burst schedule may beconfigured by the wireless communication device 101, and may includeinformation regarding burst times and satellite identification for thesebursts. The sleep schedule may be determined from the LEO burstschedule, whereas fewer bursts, satellites, and/or beams from thesatellites may be selected, monitored, or tracked, for lower accuracyposition requirements, and more bursts, satellites, and/or beamsselected, monitored, or tracked for higher accuracy positioning.

FIG. 1B is a block diagram of an exemplary dual mode global navigationsatellite system for automated syncing in accordance with an embodimentof the invention. Referring to FIG. 1B, there is shown a globalnavigation satellite system 150 comprising the wireless communicationdevice 101, MEO satellites 105, and LEO satellites 107.

The wireless communication device 101 may comprise common RF front endelements such as an antenna/low-noise amplifier (LNA)/signal splitter111. The wireless device 101 may also comprise configurable or dualMEO/LEO RF paths 113, and a processing block 115.

The configurable or dual MEO/LEO RF paths 113 may compriseamplification, down-conversion, filtering, and analog-to-digitalconversion capability for received MEO and LEO signals. The processingblock 115 may comprise one or more CPUs (e.g. a RISC CPU) fordemodulating signals and calculating positioning information, forexample. Furthermore, the processing block 115 may be operable toconfigure the number of LEO satellites 107 utilized for determiningposition. For example, if coarse location is acceptable and low powerusage is desired, LEO signal bursts from a lower number of satellitesmay be utilized.

In an example embodiment, the LEO signal path may be utilized to enhancethe geo-location capability of the MEO signal path, by extracting timinginformation and rough position information from the LEO signals duringone or multiple bursts. In this way, for example, the MEO cold starttime may be reduced to the warm start time. Thus, less time/power isspent having the MEO signal path turned on.

Furthermore, the processing block 115 may be operable to switch certainfunctionality and/or circuitry off and on based on a sleep schedule. Forexample, Rx circuitry such as the configurable or dual MEO/LEO RF paths113 may be switched off during times when the sleep schedule indicatesthat no LEO satellite bursts are to be received or MEO satellite signalsare too weak to be tracked. The sleep schedule may be configured basedon a desired accuracy, where fewer LEO bursts and/or satellites and/or alower duty cycle for tracking MEO signals may be utilized for loweraccuracy requirements. Similarly, memory blocks may be powered down whenlower accuracy, and thus lower burst count, operation is acceptable.

In an exemplary scenario, a satellite burst schedule may be configuredby the processing block 115, and may include information regarding LEOburst times and satellite identification for these bursts. The sleepschedule may be determined from the burst schedule, whereas fewerbursts, satellites, and/or beams from the satellites may be selected,monitored, or tracked, for lower accuracy position requirements, andmore bursts, satellites, and/or beams selected, monitored, or tracked,for higher accuracy positioning.

FIG. 1C is a schematic illustrating power optimization of a low Earthorbit satellite receiver, in accordance with an embodiment of theinvention. Referring to FIG. 1C, there is shown the wireless device 101,MEO satellites 105, and LEO satellites 107.

In an exemplary scenario, 2-5 bursts from one or more of the LEOsatellite 107 may be received by the wireless communication device 101over a few seconds. The burst may be down-converted and demodulated toextract an accurate clock and satellite orbital data. These may becommunicated to a position engine that may calculate the position.Furthermore, once the satellite orbital data is extracted, the Dopplershift may be calculated from the received burst intervals compared tothe actual burst intervals, which are known for each satellite.

The extracted clock may be utilized to calibrate the LO/PLL and/or TCXOtiming circuits in the wireless communication device 101. This may allowthe RF receive paths to power down more frequently, particularly the MEO(e.g. GPS) RF paths, since it would not be needed to calibrate thetiming circuits. In addition, the LEO-path derived timing calibrationmight allow the MEO signal path to be tracking satellites intermittentlyat a lower duty cycle, so as to trade off power with position accuracy.

In another exemplary scenario, the wireless communication device 101 mayreceive a code from one or more of the LEO satellites 107 that indicatesan approximate location, for example a code that indicates that thesatellite is currently over the United States, or a particular region ofthe country, which may enable the device to first establish a coarseposition, perhaps in conjunction with a previously calculated position,which may then be further zoomed in to the actual position.

In an exemplary scenario, the wireless communication device 101 mayoptimize its power usage based on the desired accuracy of the calculatedposition. Better accuracy may be obtained with multiple satellites, butthe duty cycle increases and thus results in higher power usage. Thewireless communication device 101 may be operable to choose betweenmultiple satellites for high accuracy, and thus use more power, orcoarse positioning with fewer satellites and using lower power. Thewireless communication device 101 may be operable to use the satellitewith the highest receive power, and when it disappears, the wirelesscommunication device 101 may switch to the next visible satellite withthe highest signal strength.

FIG. 1D illustrates an exemplary low Earth orbit satellite system, inaccordance with an embodiment of the invention. Referring to FIG. 1D,there is shown an LEO satellite system 180 comprising LEO satellites107, satellite error/tracking control 119, a control station 121, acustomer server 123, reference stations 125A and 125B, referencereceivers 127A and 127B, a user receiver 129, a laptop 131, and theInternet 133.

The satellite error/tracking control 119 may comprise a satellite dishfor tracking the orbits of the LEO satellites 107. Slight inaccuraciesin the satellite orbits as compared to their expected trajectories mayresult in significant positioning errors of devices that utilize the LEOsatellites 107. The control station 121 may comprise a plurality ofservers, for example, that may be operable to communicate with thesatellite error/tracking control 119, and may store orbit and satelliteand burst schedule.

The customer server 123 may comprise a server of a provider of satellitedata for customer positioning applications. Accordingly, the customerserver 123 may communicate with the control station 121 to obtaindesired orbit and satellite burst schedule data for use by users. Thecustomer server 123 may be communicatively coupled via the Internet 133to the reference stations 125A and 125B, which may be operable tocalculate reference pseudo-range and Doppler shift at referencepositions. This information may be utilized by user receivers forpositioning purposes.

The reference receivers 127A and 127B may comprise GNSS receivers forreceiving signals from MEO satellite signals. Because the position ofthe reference receivers 127A and 127B is known, the reference receivers127A and 127B and reference stations 125A and 125B may be operable toprovide accurate satellite ephemeris data for user GNSS receivers thatmay correspond to a region within a certain radius of the referencereceivers 127A and 127B.

The LEO satellites 107 may transmit time information in a burst. LEOsatellite receivers may see up to 3 satellites, and since the satellitesare low orbit, one passes overhead rather frequently, e.g., almost every15 minutes in the case of Iridium LEO satellites.

In an exemplary scenario, the reference base stations 125A and 125B maycalculate expected pseudo-range and Doppler shift, at a known referenceposition of the reference receivers 127A and 127B, for example. Thesecorrections may then be sent to the user's LEO receiver system 129,which may then subtract differential corrections from the measuredpseudo-range and Doppler shift. The differential corrections may becalculated at the reference stations 125A and 125B or locally. Thedifferential corrections may correct satellite clock errors,orbit/ephemeris errors, and atmospheric errors.

The orbit data may comprise polynomial fit coefficients (ephemerides)and geo-location parameters. In an exemplary scenario, the orbit filesmay be valid for approximately 4 hours, but updates may be availableevery hour, based on exact measurements by base stations.

A satellite burst schedule, or MDO file, may comprise the associationbetween a burst ID, the transmitting LEO satellite ID during that burstand its active beam IDs and thus may provide useful information forestimating attenuation. In an exemplary scenario, the MDO files may beavailable every 24 hours. The received and computed information may beco-related to the orbit and MDO data to compute the position of a userreceiver.

FIG. 2A is a diagram illustrating an exemplary dual mode radio frequencyreceiver, in accordance with an embodiment of the invention. Referringto FIG. 2, there is shown a receiver 200 comprising an antenna 201, alow noise amplifier (LNA) 203, a signal splitter 204, a LEO path 210, aMEO path 220, a local oscillator (LO)/phase locked loop (PLL) 211, acrystal oscillator 213, a central processing unit 219, and a register221.

The LEO path 210 and MEO path 220 may comprise similar components,configured for different frequencies as needed, such as a programmablegain amplifiers (PGAs) 207A and 207B, receive signal strength indicatormodules (RSSI) 208A and 208B, mixers 209A and 209B, filters 205A 205B,215A, and 215B, and analog-to-digital converters (ADCs) 217A and 217B.

The antenna 201 may be operable to receive RF signals for subsequentprocessing by the other elements of the receiver 200. The antenna 201may comprise a single antenna with wide enough bandwidth to receive bothLEO and MEO signals, may comprise a tunable antenna to cover the desiredfrequency range, or may comprise more than one antenna for receivingsignals, each for receiving signals in one of a plurality of frequencyranges.

The LNA 203 may be operable to provide amplification to the signalsreceived by the antenna 201, with the amplified signal beingcommunicated to the splitter 204. The LNA 203 may have a wide enoughbandwidth to amplify both MEO and LEO satellite signals.

The signal splitter 204 may be operable to communicate part of thesignal received from the antenna 201 to the LEO path 210 and part to theMEO path 220. This may be achieved by splitting the signal at a certainpercentage to each path, such as 50%/50%, for example, or may split thereceived RF signal based on frequency, such that only MEO signals arecommunicated to the MEO path 220 and only LEO signals are communicatedto the LEO path 210.

The filters 205A and 205B may comprise active or passive filters and maybe operable to attenuate signals at frequencies outside a desired rangeand allow desired signals to pass. For example, the filter 205A may passLEO satellite signals while filtering out MEO signals. The filtermodules 205A and 205B may comprise active and/or passive filters forremoving unwanted signals while allowing desired signals to pass to thePGAs 207A and 207B. In an exemplary scenario, the filter modules 205Aand 205B comprises surface acoustic wave (SAW) filters.

The PGAs 207A and 207B may provide amplification to signals receivedfrom the filters 205A and 205B, and may be configured to operate at MEOor LEO frequencies, or may operate over both frequency ranges. Forexample, the PGA 207 may be configured by a processor, such as the CPU219.

The RSSI modules 208A and 208B may comprise circuitry for determiningthe magnitude of a received signal, and may sense signal strengths atthe PGAs 207A or 207B or for down-converted signals after the filters215A and 215B, for example. Accordingly, the RSSI modules 208A and 208Bmay be operable to sense signal strength at any point along the RF pathsin the receiver 200.

The mixers 209A and 209B may comprise circuitry that is operable togenerate output signals at frequencies that are the sum and thedifference between the input RF signals and the local oscillator signalreceived from the LO/PLL 211. In an exemplary scenario, the LEO path 210and the MEO path 220 may comprise two paths each to enable the receptionof in-phase and quadrature (I and Q) signals. Accordingly, the mixers209A and 209B may each comprise two mixers, each receiving LO signalswith 90 degree phase difference to the other mixer of the pair.

In another exemplary scenario, the mixer 209 may down-convert thereceived RF signals to an intermediate frequency (IF) for furtherprocessing, as opposed to down-converting directly to baseband. In thisscenario, the filter modules 215A and 215B may comprise a bandpassfilter that is configured to pass the desired IF signals while filteringout the undesired low and high frequency signals.

The LO/PLL 211 may comprise circuitry that is operable to generate RFsignals to enable down-conversion of RF signals received by the mixers209A and 209B. The LO/PLL 211 may comprise a voltage-controlledoscillator, for example, with a PLL to stabilize the frequency of theoutput signal communicated to the mixers 209A and 209B. In an exemplaryscenario, the LO/PLL 211 may generate a plurality of LO signals fordown-converting I and Q signals in the LEO path 210 and the MEO path220.

The crystal oscillator 213 may comprise a stable clock source for thereceiver 200, and may comprise a piezoelectric crystal, for example,that outputs a stable clock signal at a given temperature. The crystaloscillator 213 may comprise a source for the various LO signals to becommunicated to the mixers via the LO/PLL 211.

The ADCs 217A and 217B may comprise circuitry that is operable toconvert analog input signals to digital output signals. Accordingly, theADCs 217A and 217B may receive baseband or IF analog signals from themixers 209A and 209B and may generate digital signals to be communicatedto the CPU 219.

The CPU 219 may comprise a processor similar to the processor 115, forexample, described with respect to FIG. 1B. Accordingly, the CPU 219 maybe operable to control the functions of the receiver 200 and may processreceived digital baseband or IF samples to demodulate, decode, and/orperform other processing techniques to the received data. Otherprocessing techniques may comprise positioning calculations based onreceived satellite signals. The CPU 219 may thus be operable todemodulate and decode both MEO and LEO satellite data, such as GPS andIridium data.

The CPU 219 may receive RSSI information from the RSSI modules 208A and208B and may control the gain of the various gain stages in the Rxpaths. Similarly, the CPU may control the LO/PLL 211 via the register221.

The register 221 may comprise a memory register for storing aconfiguration to be communicated to the LO/PLL to down-convert MEOand/or LEO signals. The register 221 may communicate an output signal tothe LO/PLL 211 that indicates the desired frequency signals todown-convert the received RF signals to IF or baseband.

In an exemplary scenario, the receiver 200 may be operable to receiveboth MEO and LEO satellite signals for positioning purposes. In thismanner, the wireless device that comprises the receiver 200 may becapable of determining its position even within a structure thatattenuates GPS signals. Accordingly, a plurality of positioning-basedapplications may be performed. For example, the positioning function maybe operable to power on and off WiFi circuitry based on the knownlocations of trusted WiFi networks and a determined position of thewireless device using LEO satellite signals.

In an exemplary scenario, 2-5 bursts from the LEO satellite may bereceived by the wireless device over a few seconds. The bursts may bedown-converted and demodulated to extract an accurate clock andsatellite orbital data. These may be communicated to a position enginethat may calculate the position. Furthermore, once the satellite orbitaldata is extracted, the Doppler shift may be calculated from the receivedburst intervals compared to the actual burst intervals, which are knownfor each satellite.

The extracted clock may be utilized to calibrate the LO/PLL 211 and/orTCXO timing circuits 213 in the wireless communication device 101. Thismay allow the RF receive paths 210 and 220 to power down occasionally,particularly the MEO (e.g. GPS) RF path 220, since it would not beneeded to calibrate the timing circuits. In addition, the LEO-pathderived timing calibration might allow the MEO signal path to betracking satellites intermittently at a lower duty cycle, so as to tradeoff power with position accuracy.

In yet another exemplary scenario, the receiver 200 may enable MEO andLEO positioning to switch certain functionality and/or circuitry off andon based on a sleep schedule. For example, the Rx circuitry 210 and 220may be switched off during times when the sleep schedule indicates thatno LEO satellite bursts are to be received or MEO satellite signals aretoo weak to be tracked. The sleep schedule may be configured based on adesired accuracy, where fewer LEO bursts and/or satellites and/or alower duty cycle for tracking MEO signals may be utilized for loweraccuracy requirements. Similarly, memory blocks may be powered down whenlower accuracy, and thus lower burst count, operation is acceptable.

FIG. 2B is a block diagram illustrating a dual-mode time-division duplexsatellite receiver, in accordance with an embodiment of the invention.Referring to FIG. 2B, there is shown an exemplary receiver 200comprising an antenna 201, a low-noise amplifier (LNA) 203, ananalog-to-digital converter (A/D) 217, a buffer 251, and two paths, aMEO path 250, and a LEO path 260. There is also shown a blanking/switchmodule 259, a LO/PLL 261 and a central processing unit (CPU) 267.

The MEO path 250 may comprise a sample and hold (S/H) module 253, a GNSSacquisition module 255, and a GNSS tracking module 257. The S/H module253 may be operable to sample the digital signal from the buffer 251,and hold the sampled value for a configurable time, which may becommunicated to the GNSS acquisition module 255 and the GNSS trackingmodule 257. The S/H module 253 may thus act as a gatekeeper for data tothe GNSS acquisition module 255 and the GNSS tracking module 257. Thismay enable the receiver 250 to switch between MEO and LEO signalswithout losing a MEO value when receiving LEO signals, for example, andavoid the divergence of the output of the GNSS acquisition module 255and the GNSS tracking module 257. In another exemplary scenario, the S/Hmodule 253 may output a constant value, a string of zeroes, for example,or any known pattern to avoid divergence of the output of the GNSSacquisition module 255 and the GNSS tracking module 257.

The GNSS acquisition module 255 may be operable to acquire a lock to oneor more GNSS satellites, which may allow the GNSS tracking module 257 todetermine and track the location of the receiver. The GNSS acquisitionmodule 255 may detect MEO frequency signals above a threshold signalstrength and extract an accurate clock by determining the code-divisionmultiple access (CDMA) coarse acquisition (C/A) code for the receiveddata. A determined satellite ID and C/A code may be used by the GNSStracking module 257 for accurate positioning purposes.

Similarly, the LEO path 260 may comprise a filter 263 and a LEO timingsignal demodulator module 265. The LEO timing signal demodulator module265 may receive filtered LEO signals from the filter 263 and maydemodulate the received signal to an accurate clock from thetransmitting satellite. This accurate clock along with informationregarding the satellite orbit may be utilized for positioning. In thismanner either MEO or LEO signals, or both, may be utilized forpositioning purposes.

The LEO timing demodulator 265, the GNSS acquisition module 255, and theGNSS tracking module 257 may communicate output signals to the CPU forfurther processing or use of the determined timing and/or positioningdata.

The blanking/switching module 259 may be operable to provide the TDDfunction for the receiver, switching the LEO path 260 on and off andblanking the MEO path 250 by configuring the output of the S/H module253 to retain the previous data to the GNSS acquisition module. TheLO/PLL 261 may provide a timing signal for the blanking/switch module.

The filter 263 may be operable to filter out unwanted signals allowingthe desired satellite RF signal to pass to the LEOT demodulator module265. The LEO timing demodulator may be operable to extract an accuratetiming signal from the received LEO signals, which along with satelliteephemeris data, may be utilized by the CPU 267 for positioning purposes.

FIG. 3 is a schematic illustrating an exemplary satellite selectionsystem, in accordance with an embodiment of the invention. Referring toFIG. 3, there is shown satellite selection system 300 an antenna 301, anRF module 303, a LEO satellite signal demodulation module 305, and aposition engine 307. The RF module 303 may comprise circuitry forreceiving, amplifying, and down-converting received satellite signals.The RF module 303 may be communicatively coupled to the LEO demod module305 for subsequent demodulation.

The LEO demod module 305 may comprise suitable circuitry, logic, and/orcode for tracking LEO satellite bursts and may comprise a sort engine305A. The sort engine 305A may comprise a sort algorithm for determiningwhich satellites the wireless device 101 may utilize for positioningpurposes.

The position engine 307 may comprise suitable circuitry, logic, and/orcode for calculating a global position based on received satellitesignals demodulated by the LEO demod module 305. The position engine 307may also be operable to communicate a relevance factor 309 to the sortmodule 305A in the LEO demod module 305.

In operation, the antenna 301 may receive satellite signal bursts from aplurality of LEO satellites 107, the RF module 303 may amplify, filter,and down-convert the received signals to baseband, and the LEO demodmodule 305 may demodulate the down-converted signals to extractsatellite ID codes, clocks, and other data relevant to positioning.

Intervals between bursts may comprise possible sleep times in which theRF module 303 and the demodulation circuitry 305 may be powered down.The sort engine 305A in the LEO demod module 305 may receive a relevancefactor 309 from the position engine 307, where the relevance factor 309may specify the relevance of a given satellite signal for calculatingposition. The relevance factor 309 may be inversely proportional to anaccuracy range from the calculated position and may be based on how thefilter converges in the positioning calculation in the position engine307. If the relevance is approximately 1, it contributes greatly toposition accuracy, and if the relevance is approximately 0, it does notcontribute significantly. In another embodiment, the position engine 307may output a list of visible satellites sorted by the highest to lowestimpact on position accuracy.

The sort algorithm utilized by the sort module 305A may be based on userconfiguration input and/or the relevance factor 309. The userconfiguration 305C may comprise a low power mode or a high accuracymode, where in the low power mode, only satellites with a high or ahighest modulated signal to noise ratio (C/N) 305B are used for a periodof time, T_(conf). During a select period, T_(select), all satellitebursts may be considered to pick the high or highest C/N satelliteand/or to discard satellites with low relevance. This relevanceinformation may be fed back from the position engine 307. Furthermore,the algorithm may be forced to use a particular satellite or satellitesby user configuration 305C or based on position engine feedback.Exemplary timing diagrams are illustrated in FIGS. 5 and 6.

The position engine 307 may calculate the position with all incomingbursts and extract latitude, longitude, and position error covariance.The position engine 307 may iterate the position calculation by removingsatellites, and repeat with all combinations of the satellites in view.The results may be sorted by relevance—i.e., which satellite burstcombination gives the most accurate position. The resulting relevancefactor 309 may be fed back to the sort engine 305A at baseband todiscard low relevance satellites and thus save power. This process maybe an iterative process in software or a combination of software andhardware, and the position engine 307 may be configured to extractsatellite relevance in a shorter iteration.

FIG. 4 is a schematic illustrating a timing diagram for low Earth orbitsatellite signals, in accordance with an embodiment of the invention.Referring to FIG. 4, there is shown a satellite timing diagram 400comprising four LEO satellite signal bursts 401A-401D separated in timeby the burst intervals 403A-403C. In an exemplary scenario, a dual modeor time-division duplexed MEO/LEO RF receiver may receive the LEO burstsand demodulate them to obtain the satellite ID and the clock frequencyoffset. From the satellite ID, the receiver then has knowledge of thatsatellite's expected burst interval. By comparing the expected burstinterval to the measured interval, the receiver then may calculate aDoppler shift. Each of these pieces of information may be utilized toassist the MEO position calculation (e.g. GPS). Alternatively, the LEOsatellite signal burst calibration may be utilized to keep the receiverTCXO calibrated while leaving the MEO (GPS) system powered down.

FIG. 5 is a timing diagram illustrating signal bursts from threesatellite vehicles, in accordance with an embodiment of the invention.Referring to FIG. 5, there is shown pulses from satellites S₁, S₂, andS₃ versus time, labeled as timing diagrams 510, 520, and 530. The timingintervals t₁, t₂, and t₃ may represent intervals where RF and demodcircuitry may be powered down, depending on how many of the visiblesatellites are being utilized. For example, if only S₁ is beingutilized, the circuitry may be powered down for most of the interval t₁,depending on how quickly circuitry may be powered down and back up.

FIG. 6 is a timing diagram of signal bursts from three satellites withvarying signal strengths, in accordance with an embodiment of theinvention. Referring to FIG. 6, there is shown pulses corresponding tosignal bursts from satellites S₁, S₂, and S₃ where the height of thepulses is proportional to the signal to noise ratio, or C/N, whichindicates the carrier signal to noise ratio, for example. There is alsoshown satellite select intervals, T_(select) 601A and 601B, andT_(config) 603.

During the select period, T_(select) 601A, all of the bursts may bereceived and measured to determine a C/N and relevance factor, and RFcircuitry and demod circuitry may be powered down between bursts.

In an exemplary scenario, during the config interval, T_(config) 603,the system may only track the selected satellite that had the strongestsignal and relevance. Accordingly, where the S₃ satellite exhibits thehighest C/N during the T_(select) interval 601A, the S₃ satellite may beutilized for positioning purposes during the T_(config) interval 603.

The highest strength signals may be reassessed during each selectinterval as signal strengths vary as the satellites move through theirorbits. Accordingly, if, during the next T_(select) interval 601B, theS₃ C/N decreases below that of the S₁ C/N, the S₁ satellite signal maybe utilized for positioning purposes during the next T_(config)interval, not shown.

FIG. 7 is a flow diagram illustrating an exemplary satellite signalselect process, in accordance with an embodiment of the invention.Referring to FIG. 7, in step 703, after start step 701, a monitoringtimer may be started that tracks the time spent monitoring satellitesignal strength. In step 705, the signal strength of visible satellitesmay be monitored, followed by step 707 where a timer may be started thattracks the time at which circuitry is powered down and when it will bepowered back up for the next burst of the selected satellite orsatellites.

In step 709, if the sleep timer has not expired, the process may remainin step 709. Once the sleep timer has expired, the process may proceedto step 711 where the monitoring timer may be compared to the timeT_(Select). If the monitoring timer has not exceeded this time, theexemplary steps may loop back to step 705 for further satellitemonitoring. If the monitoring timer has passed the time Tselect, thedecoding timer may be started in step 715, which may monitor the timespent decoding received satellite signals.

In step 717, the received satellite signals may be decoded forpositioning purposes. The sleep timer may be started in step 719, suchthat in step 721, if the sleep timer has not expired, the example stepsmay remain in step 721. Once the sleep timer has expired, the processcontinues with step 723, where the decoding timer may be compared toT_(Config). If it has not exceeded T_(Config), the process may step backto step 717 to continue decoding satellite signals.

In step 725, if the timer indicates that the T_(config) interval is overand it has progressed to a T_(select) interval, the process may proceedto step 725 to determine whether to power down or not. If not, theprocess repeats the entire process from step 703, and if so, powers downin step end step 727.

FIG. 8 illustrates exemplary steps for power saving in a low Earth orbitsatellite positioning receiver, in accordance with an embodiment of theinvention. Referring to FIG. 8, after start step 801, in step 803, thewireless device may receive a satellite burst table from a host server,for example. The table may comprise satellite beam and burst informationthat may be valid for a specific time frame in a specific geographicregion based on the known satellite trajectories at any specific time,as determined by a real time clock.

In step 805, the wireless device may determine a desired positioningaccuracy and power usage. For example, 100 meter accuracy may besuitable for navigating from one city to another, whereas accuracy of afew meters may be desired for short range navigation. Better accuracy isobtained by utilizing more satellites for positioning purposes, andconversely, lower power is used for lower accuracy positioning.Accordingly, if the wireless device has a nearly depleted battery butthe user still wishes to determine their location, the wireless devicemay be configured for a lower accuracy positioning.

Based on the desired accuracy and/or power usage, in step 807 thewireless device may generate a sleep schedule that may be derived from asmall subset of the received satellite burst table for lower accuracypositioning, or from a larger subset of the burst table for higheraccuracy positioning. If optimal accuracy is desired, the entire bursttable may be used to derive the sleep schedule.

In step 809, the wireless device may cycle positioning circuitry, suchas the RF receiver, IF processing blocks, and the CPU, on and off basedon the sleep schedule. The wireless device may utilize a real time clockto determine when blocks should be switched on or off. This is followedby end step 811.

FIG. 9 illustrates exemplary steps for satellite positioning receiversleep scheduling, in accordance with an embodiment of the invention. Instep 903, after start step 901, a reading of the real time clock (RTC)of the wireless device is performed. The RTC is then used to calculatethe L-band frame count (LBFC), i.e., the LEO system-defined timestamp,corresponding to desired bursts in the satellite burst table. In step905, RF receiver circuitry and the intermediate frequency (IF) blocksmay then be powered up for desired bursts, followed by step 907 wherethe IF in-phase and quadrature (I and Q) samples may be collected. Instep 909, the LBFC may be incremented accordingly.

In step 911A, the sleep schedule may be received from a host based onthe time or LBFC. In another exemplary scenario, the sleep schedule maybe generated by the wireless device. In step 911, the received orgenerated sleep schedule may be utilized to determine whether the Rxcircuitry is to be powered down, and if not, the process may continuewith further I and Q sample collection in step 907. If the sleepschedule indicates that no bursts are to be received, the exemplarysteps may proceed to step 913 where the RF circuitry and IF block may bepowered down to wait until the next Rx slot in step 915. In step 917,the LBFC may be incremented based on the time slept, before the RFcircuitry and IF block are powered back up in step 905.

In parallel to the RF circuitry and IF block sleep scheduling, memorymay also be configured according to a sleep schedule in step 919. When Iand Q samples are collected, memory may be allocated to the samples andsent to the burst decoder in step 925. If the memory bank is off, it maybe powered up to store the collected samples.

The burst may be decoded and if, in step 927, bursts have not beenreceived for the entire last 2 seconds, for example, this indicates thatthe receiver may have lost track of time and is not synced to the Rxslot. The process would then proceed back to the reading of the RTC andcalculation of the LBFC in step 903.

If bursts were received for the entire two seconds in step 927, theprocess would continue as normal where unused memory may be freed up forother purposes and/or powered down in step 929, followed by the decodedburst being communicated to the geo-location engine for positioningcalculation in step 931.

Also in parallel to the RF circuitry and IF block sleep scheduling, theCPU may be put into sleep mode when no higher priority tasks arewaiting, as illustrated in steps 933, 935, and 937. The CPU or otherprocessor may remain in a sleep state when no high priority tasks aredue for processing. In step 935, when a high priority task is received,the processor may wake and perform the task in step 937 before returningto sleep in step 933. The sleep schedule may correlate to the receivedor generated sleep schedule of the wireless device.

FIG. 10 is a block diagram illustrating an exemplary LEO satellitereceiver information flow, in accordance with an embodiment of theinvention. The sleep scheduler 1007 in the receiver may select whichbursts to receive based on the accuracy of position needed by thereceiver. This information is communicated to firmware 1005 that isutilized to control the operation of the RF circuitry and IF blocks, asdescribed with respect to FIGS. 2A and 2B. The resulting decoded burstsmay then be communicated to the geo-location engine 1001, which may alsoreceive the MDO file, or satellite burst table 1003.

FIG. 11 is a block diagram illustrating an LEO exemplary satellite framesequence, in accordance with an embodiment of the invention. Thedifferent blocks correspond to bursts from a single satellite, while thedifferent shades of blocks indicate different beam-sectors (panels) of asingle satellite. Each satellite has 48 beams arranged as 16 beams in 3panels. Each row of blocks corresponds to 16 consecutive bursts, eachtransmitted within an L-band frame; in total 48 frames are shownstarting from to Frame X, Frame X+47. The LEO satellite bursts may bescheduled based on location accuracy needed and power usage. The currentbroadcast plan may schedule a burst to be transmitted from a singlesatellite beam on an average of every 1.44 seconds, which may be basedon a 3 burst/frame/satellite repeat rate (i.e., three bursts transmittedsimultaneously from three satellite beams per frame).

The three bursts may arrive at the same time from three beams—so burstsmay be overlapping but targeted for different geo locations. If thereceiver is located in-between two beam locations, it would be morelikely to see both bursts and bursts from the same satellite onconsecutive frames.

To cover all 48 beams/satellite, each beam would burst on average every48/3 frames which is 16 frames (16*90 ms=1.44 seconds). The actualimplementation, however, may not be uniform due to historical or legacyfactors. Thus, instead of every 16 frames, a beam may cycle, forexample, as 14 frames between burst 1 and burst 2, 18 frames betweenbursts 2 and 3 and 16 frames between bursts 3 and 1 (pattern repeats onthis 3 burst ‘super-cycle’). Beams 1-16 may be in one panel, 17-32 inanother, and 33-48 in another, for example.

An exemplary script that controls the LEO satellite burst schedule on aLEO satellite for 3 bursts/frame/satellite repeat rate may be given by:

{{10, 13, 12}, {26, 29, 28}, {42, 45, 44}, {9, 1, 11}, {25, 17, 27},{41, 33, 43}, {8, 5, 15}, {24, 21, 31}, {40, 37, 47}, {6, 4, 16}, {22,20, 32}, {38, 36, 48}, {3, 7, 14}, {19, 23, 30}, {35, 39, 46}, {5, 12,9}, {21, 28, 25}, {37, 44, 41}, {2, 11, 13}, {18, 27, 29}, {34, 43, 45},{1, 15, 10}, {17, 31, 26}, {33, 47, 42}, {48, 35, 38}, {16, 3, 6}, {32,19, 22}, {28, 24, 20}, {12, 8, 4}, {44, 40, 36}, {27, 25, 23}, {11, 9,7}, {43, 41, 39}, {30, 18, 21}, {14, 2, 5}, {46, 34, 37}, {29, 26, 17},{13, 10, 1}, {45, 42, 33}, {31, 22, 24}, {15, 6, 8}, {47, 38, 40}, {23,32, 19}, {7, 16, 3}, {39, 48, 35}, {20, 30, 18}, {4, 14, 2}, {36, 46,34}};

Each set has three beam numbers since the same burst may be transmittedon three beams, and there may be 48 such sets, after which the patternrepeats.

An exemplary script that controls the LEO satellite burst schedule for 2bursts/frame/satellite repeat rate (i.e., two bursts transmittedsimultaneously from two satellite beams per frame) may be given by:

{{1, 7}, {17, 23}, {33, 39}, {2, 11}, {18, 27}, {34, 43}, {3, 12}, {19,28}, {35, 44}, {5, 13}, {21, 29}, {37, 45}, {4, 14}, {20, 30}, {36, 46},{6, 9}, {22, 25}, {38, 41}, {8, 15}, {24, 31}, {40, 47}, {10, 16}, {26,32}, {42, 48}, {39, 33}, {7, 1}, {23, 17}, {27, 18}, {11, 2}, {43, 34},{28, 19}, {12, 3}, {44, 35}, {29, 21}, {13, 5}, {45, 37}, {30, 20}, {14,4}, {46, 36}, {25, 22}, {9, 6}, {41, 38}, {31, 24}, {15, 8}, {47, 40},{32, 26}, {16, 10}, {48, 42}};

Each set has two beam numbers because the same burst may be transmittedon two beams, and there may be 48 such sets, after which the patternrepeats.

The rate at which a LEO satellite receiver receives bursts may beaffected by factors such as a beam possibly not bursting as scheduled orother factors that can actually increase the number of bursts per ˜1.5seconds. The receiver should see bursts from other satellites, up tothree in general. Therefore, with the varying arrival times due togeometry, the receiver should see more than one burst per ˜1.5 secondson average.

The receiver may also see the adjacent beams from the same satellite,just as the receiver would pick up beams from other satellites. Thus,the least a receiver would see is only one beam from one satellite onaverage every 1.44 seconds approximately. The longest time betweenbursts on a particular beam for one super-cycle may be 18 frames, or1.62 seconds.

Each satellite may transmit a burst out of a given beam on average every1.5 seconds and the bursts occur on 90 ms frame boundaries, while thereceiver may see up to three satellites. The opportunities fortransmitting a burst are fixed. But the actual bursts transmitted dependon the satellite power load and other scheduling factors.

In an exemplary scenario, each burst may be 20 ms long. The satellitesmay be in sync but their clocks may typically vary by a fewmicroseconds. The range to the satellites can create differences in timeof arrival of about 10 ms. The bursts typically don't overlap, but ifthey do, as long as their Doppler shift is different enough or one ismuch stronger than the other satellite, both signals may be extractedwith some degradation.

If the power of the bursts were to be increased, it likely would changethe 3 burst/frame/satellite repeat rate of ˜1.44 s to 2burst/frame/satellite at approximately 2.16 seconds, which would be ˜0.5second delta between bursts from a given satellite beam in the worstcase.

Since the burst arrival times are predetermined, the wireless device mayhave functionality in software, for example, to shut down the receiverand save power for battery based systems. The receiver may alsointelligently decide which satellites and beams to look for andselectively turn on the receiver based on the burst schedule in thesatellite burst schedule data files. An exemplary burst schedule isshown in FIG. 12.

FIG. 12 is an exemplary satellite burst schedule, in accordance with anembodiment of the invention. In an exemplary scenario, there may be 48beams in each LEO satellite. The beam number is one of the columns ofthe satellite burst data table. Beams 1-16 are in one panel, 17-32 inanother, and 33-48 in another. In instances where lower positioningaccuracy is acceptable, a subset of the bursts may be selected to bereceived. Accordingly, RF circuitry and IF blocks may be powered off andon according to a sleep schedule configured based on the satellite burstschedule data file and desired positioning accuracy and power usage.

An accuracy policy may be determined based on assumptions such as LEOsatellites and beams being synchronized to a 90 ms clock and with burstarrival times being off by 2 to 12 ms based on the distance between thesatellite and receiver. In addition, the satellites may transmit thesame timing burst from three beams pointing to different areas. Onestrong burst may be received at the receiver location as well as faintor low energy bursts of the other beams. The Doppler shifts would bedifferent so they would not interfere with each other, even though theyoverlap. This may also occur if beams from other satellites aretransmitting during the same burst.

The geo-location may be computed with just one satellite, but theaccuracy would likely be low. Knowing the receiver altitude would helpincrease the accuracy. The geo location engine filter may need manybursts, up to 20 for example, to get reasonable position accuracy. Oncethe position is computed, even if the receiver is not receivingsubsequent bursts, the position accuracy may not degrade if the receiveris not in motion. In an example scenario, an accelerometer may beutilized to determine whether the wireless device is in motion. Each ofthese factors may be utilized to determine which bursts are importantand balance the RF circuitry and IF block sleep schedule.

In an embodiment of the invention, a method and system may comprisereceiving LEO RF satellite signals utilizing a LEO satellite signalreceiver path 113, 210, 260 in a wireless communication device 101.Circuitry in the LEO satellite signal receiver path 113, 210, 260 may beconfigured in a powered down state based on a sleep schedule. A locationof the wireless communication device 101 may be determined utilizing LEOsignals received by the LEO satellite signal receiver path 113, 210,260.

The sleep schedule may be based on a desired accuracy of the determinedlocation. The sleep schedule may be based on relative strengths C/N ofsignals received from a plurality of LEO satellites 107. The relativestrengths of received signals, C/N, may be compared utilizing a sortmodule 305A in a LEO demodulator 305 in the LEO satellite signalreceiver path 113, 210, 260.

The sleep schedule may be based on a relevance factor 309 generated by aposition engine 307 and communicated to the sort module. The sleepschedule may be received from a server. The sleep schedule may be basedon a desired power level of the wireless communication device 101. Thewireless communication device 101 may comprise a medium Earth orbitsatellite signal receiver path 220, 250. In-phase and quadrature signalsmay be processed in the LEO satellite signal receiver path 113, 210,260. The wireless communication device 101 may be controlled by areduced instruction set computing (RISC) central processing unit (CPU)115, 219, 267.

Other embodiments of the invention may provide a non-transitory computerreadable medium and/or storage medium, and/or a non-transitory machinereadable medium and/or storage medium, having stored thereon, a machinecode and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform the steps as described herein for poweroptimization of a global navigation satellite system.

Accordingly, aspects of the invention may be realized in hardware,software, firmware or a combination thereof. The invention may berealized in a centralized fashion in at least one computer system or ina distributed fashion where different elements are spread across severalinterconnected computer systems. Any kind of computer system or otherapparatus adapted for carrying out the methods described herein issuited. A typical combination of hardware, software and firmware may bea general-purpose computer system with a computer program that, whenbeing loaded and executed, controls the computer system such that itcarries out the methods described herein.

One embodiment of the present invention may be implemented as a boardlevel product, as a single chip, application specific integrated circuit(ASIC), or with varying levels integrated on a single chip with otherportions of the system as separate components. The degree of integrationof the system will primarily be determined by speed and costconsiderations. Because of the sophisticated nature of modernprocessors, it is possible to utilize a commercially availableprocessor, which may be implemented external to an ASIC implementationof the present system. Alternatively, if the processor is available asan ASIC core or logic block, then the commercially available processormay be implemented as part of an ASIC device with various functionsimplemented as firmware.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext may mean, for example, any expression, in any language, code ornotation, of a set of instructions intended to cause a system having aninformation processing capability to perform a particular functioneither directly or after either or both of the following: a) conversionto another language, code or notation; b) reproduction in a differentmaterial form. However, other meanings of computer program within theunderstanding of those skilled in the art are also contemplated by thepresent invention.

While the invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiments disclosed, but that the present inventionwill include all embodiments falling within the scope of the appendedclaims.

What is claimed is:
 1. A method for wireless communication, the methodcomprising: in a wireless communication device having a low Earth orbit(LEO) satellite signal receiver path: receiving LEO RF satellite signalsutilizing said LEO satellite signal receiver path; determining alocation of said wireless communication device utilizing said receivedLEO RF satellite signals received by said LEO satellite signal receiverpath; and configuring circuitry in said LEO satellite signal receiverpath in a powered down state when said circuitry is not needed forreceiving LEO RF satellite signals, based on a sleep schedule, saidsleep schedule being based at least in part on satellite availabilityinformation received from a reference receiver external to said wirelesscommunication device and on relative strengths of signals received froma plurality of LEO satellites, said relative strengths comparedutilizing a sort module in a LEO demodulator in said LEO satellitesignal receiver path.
 2. The method according to claim 1, wherein saidsleep schedule is based on a desired accuracy of said determinedlocation.
 3. The method according to claim 1, wherein said sleepschedule is based on a relevance factor generated by a position engineand communicated to said sort module.
 4. The method according to claim1, wherein said sleep schedule is received from a server.
 5. The methodaccording to claim 1, wherein said sleep schedule is based on a desiredpower level of said wireless communication device.
 6. The methodaccording to claim 1, wherein said sleep schedule is based on a batterylevel in said wireless device.
 7. The method according to claim 1,wherein said wireless communication device also comprises a medium Earthorbit satellite signal receiver path.
 8. The method according to claim1, comprising processing in-phase and quadrature signals in said LEOsatellite signal receiver path.
 9. The method according to claim 1,wherein said wireless communication device is controlled by a reducedinstruction set computing (RISC) central processing unit (CPU).
 10. Asystem for wireless communication, the system comprising: one or morecircuits for use in a wireless communication device comprising a lowEarth orbit (LEO) satellite signal receiver path, said one or morecircuits being operable to: receive LEO RF satellite signals utilizingsaid LEO satellite signal receiver path; determine a location of saidwireless communication device utilizing said received LEO RF satellitesignals received by said LEO satellite signal receiver path; andconfigure circuitry in said LEO satellite signal receiver path in apowered down state when not needed for receiving LEO RF satellitesignals, based on a sleep schedule, said sleep schedule being based atleast in part on satellite availability information received from areference receiver external to said wireless communication device and onrelative strengths of signals received from a plurality of LEOsatellites, said relative strengths compared utilizing a sort module ina LEO demodulator in said LEO satellite signal receiver path.
 11. Thesystem according to claim 10, wherein said sleep schedule is based on adesired accuracy of said determined location.
 12. The system accordingto claim 10, wherein said sleep schedule is based on a relevance factorgenerated by a position engine and communicated to said sort module. 13.The system according to claim 10, wherein said sleep schedule isreceived from a server.
 14. The system according to claim 10, whereinsaid sleep schedule is based on a desired power level of said wirelesscommunication device.
 15. The system according to claim 10, wherein saidsleep schedule is based on a battery level in said wireless device. 16.The system according to claim 10, wherein said wireless communicationdevice also comprises a medium Earth orbit satellite signal receiverpath.
 17. The system according to claim 10, wherein said wirelesscommunication device is controlled by a reduced instruction setcomputing (RISC) central processing unit (CPU).
 18. A system forwireless communication, the system comprising: one or more circuits foruse in a wireless communication device comprising a medium Earth orbit(MEO) satellite signal receiver path and a low Earth orbit (LEO)satellite signal receiver path, said one or more circuits being operableto: receive LEO RF satellite signals utilizing said LEO satellite signalreceiver path and MEO RF satellite signals utilizing said MEO satellitesignal receiver path; determine a location of said wirelesscommunication device utilizing MEO signals received by said MEOsatellite signal receiver path and LEO signals received by said LEOsatellite signal receiver path; and configure circuitry in said LEOsatellite signal receiver path or said MEO satellite signal receiverpath in a powered down state when not needed for receiving RF satellitesignals, based on a sleep schedule, said sleep schedule being based atleast in part on satellite availability information received from areference receiver external to said wireless communication device and onrelative strengths of signals received from a plurality of LEOsatellites, said relative strengths compared utilizing a sort module ina LEO demodulator in said LEO satellite signal receiver path.
 19. Thesystem according to claim 18, comprising configuring said MEO satellitesignal receiver path when a signal strength of said received MEOsatellite signals falls below a threshold level.
 20. The systemaccording to claim 18, comprising configuring said MEO satellite signalreceiver path in an intermittent low power state based on said receivedLEO RF satellite signals.